Tisei said Saturday the timing is not right for him to campaign in the June 25 special election. Former Sen. Scott Brown also has said he will not seek the post. Others Republicans considering a race include former Lt. Gov. Kerry Healey, state Rep. Daniel Winslow and ex-Navy Seal Gabriel Gomez.

Middlesex County District Attorney Gerard Leone, a Democrat, said he may run for the post.

"Recently he has been urged by people he thinks highly of to consider a run for the senate and that's what he plans to do," a statement from his office said.

Congressmen Edward Markey and Stephen Lynch are also seeking the party's nomination.